The invention is generally applicable in the field of gas generation, where a gasification medium is introduced into the process through a rotary grid. The invention finds particular applicability in solid bed pressure generators.
The introduction of material to be reacted in rotary grid generators as a rule is carried out through the rotary grid which simultaneously serves as means for removal of ash in the reacting fuel layer. This rotary grid is as a rule a conical or cone-shaped hollow body of heat-resistant cast steel, to which the fuel is introduced over one or more centrally-arranged input conduits or pipes. The fuel then enters the reaction chamber through openings in the conical surface of the grid. In large reactors, and in particular in pressure gas generators, in which for insertion of the grid into the reactor only comparatively small openings with respect to the reactor diameter are present, annular segments in multiple levels form the grid. For optimal operation of the process system through a uniform distribution of the gasification medium through the openings in the surface of the grid it is necessary that the hollow body formed from the annular segments remain sealed at the butt-joints, so that no uncontrolled gasification medium input occur at these, which would negatively influence the efficiency of the reaction. On account of the high thermal and mechanical charging of the rotary grids, they are generally subjected to deformations of the segments, so that gaps form at the joints through which the gasification med. can pass.
As the uniform distribution of gasification medium in high-capacity generators is obtained through the force of high pressure differences between the grid interior and the reactor, already with the small gaps as may develop in the assembly the distribution is disturbed. Through this the distribution of the gasification medium is not longer uniform over the reactor cross section, leading to significant disturbances in operation of the generator which can only be overcome through replacement of the rotary grid. Complicated methods have been devised accordingly for sealing of the segments, yet these have not proved sufficient over extended operation periods.
It has further been suggested, for example according to DD-WP C 10j/198 286, to minimize the heat sensitivity of the rotary grid through protective coatings of fireproof material so that there is no deformation of the segments. In addition to the negative effect on ash removal on account of the altered coefficient of friction between ash and rotary grid, these protective coatings are also ineffective after extended contact with very hot ash, as on the inner side of the rotary grid, on account of the large hollow chamber, such low speeds of the gasification medium and thus low heat transfer coefficients are obtained, that there is hardly any difference in the thermal sensitivity of the rotary grid over time.